Icemaker drive with overload release

ABSTRACT

A turntable type ice cube maker in which a series of pivoted dumping cups having water-fill, freeze, and dump stations is revolved by a gearmotor drive affording overload protection. This protection can be called into play in the instance, for example, when the turntable rotary mechanism jams on a piece of stray ice. No excessive torque will be encountered if and as the mechanism thereupon stalls out, because of overload protection provided by a permanent-magnet clutch, interposed in the drive line from the motor of the gearmotor to the gearing thereof being protected. A most important factor is that the clutch, which continually slips while stalled out, is consistently exerting maximum rated stall torque in the drive direction for immediate restart of the mechanism as soon as the impediment causing jamming is dislodged, and a further factor is that the clutch while so slipping is in actuality exerting cycles which pulse, tending to release and even to dislodge the impediment in some cases.

ICEMAKER DRIVE WITH OVERLOAD RELEASE I 151 3,659,128 1451 Apr. 25, 1972 [57] ABSTRACT A turntable type ice cube maker in which a series of pivoted [72] Inventor; August Danek, Crystal Lake L dumping cups having water-fill, freeze, and dump stations is revolved by a gearmotor drive affording overload protection. Assigneei Auml'ol Corporation, Crystal Lake, This protection can be called into play in the instance, for ex- [22] Filed; Nov 17, 1969 ample, when the turntable rotary mechanism jams on a piece of stray ice. No excessive torque will be encountered if and as [21] Appl' 877,324 the mechanism thereupon stalls out, because of overload protection provided by a permanent-magnet clutch, interposed in 52 us. c1 ..310/99, 310/103 the drive line from the motor of the searmowr the gearing [51] Int. Cl. ..H02k 7/10 thereof being protected- A important factor is that the [58] Fi ld of Search ..62/345, 233, 137, 135; 310/41, clutch, which continually slips while stalled out, is consistently 310/103, 99, 162 exerting maximum rated stall torque in the drive direction for immediate restart of the mechanism as soon as the impedi- [56] References Cited ment causing jamming is dislodged, and a further factor is that the clutch while so slipping is in actuality exerting cycles UNITED STATES PATENTS which pulse, tending to release and even to dislodge the im- 280,322 6/1883 Nash ..310/99 ux pedimem in some cases- 2,452,945 11/1948 McCabe 3,253,169 5/1966 Haydon et a1 ..310/156 8 Clams 7 Drawmg F'gms Primary Examiner-D. X. Sliney Attorney-John W.-Gaines 84 "fill llll l ll filllllll'f' 11 II I illlllllllllll II II II "Ill ICEMAKER DRIVE WITH OVERLOAD RELEASE This invention relates to an overload release type drive for an ice cube maker, in which gearmotor gearing in a drive line provided between the motor of the gearmotor and the driven icemaker being revolved is protected against damage from overload. It particularly relates to a permanent magnet clutch interposed in the drive line and effectively slipping, whenever an overload temporarily or otherwise stalls out the clutch, in a manner to exert consistently maximum rated stall torque for restarting, and effectively magnetically recoupling automatically for resumption of power transmission upon resumption of load commensurate to the torque rating aforesaid.

My overload release coupling has general application, application for instance in the drives of revolving turntable type and paddle ejector type icemakers and other mechanism. But revolving type and paddle type icemakers form no per se part of my invention.

Ice cube makers are caused to revolve at low speeds in known way by means of a small motor connected thereto through many stages of gear reduction. While providing a drastically reduced output speed compared to running speed of the small drive motor, the reduction gears at the same time provide proportionally increased torque which, due to the torque multiplication inherent in a multistage gear train, can strip gears.

A problem I have encountered after sustained observations made of icemakers is that the mechanism sometimes jams on ice, tending to bring the motor and gearing to a dead stop. The problem is aggravated in the case, for instance, of the automatic ice cube maker provided in a home refrigerator, because the jammed condition of the mechanism may last for as long as two or three weeks before the condition is detected and the jammed in impediment is dislodged. The cause of the condition can be a stray piece of ice, such as a cube which is to be dumped and wont eject, or an ejected cube which clogs by unwantedly bouncing back into the mechanism. Naturally, the gearing in the final stages of the train is made the heaviest and provides the strongest teeth in the train. But, if the gearing is stopped, the motor will nevertheless continue to run, and gear teeth will be stripped in the final stage or stages.

The protection afforded by my invention materially reduces or substantially eliminates the foregoing problem because the clutching is effected by an elastically loaded, noncontact coupling, as will now be described in detail. Features, objects, and advantages will either be specifically pointed out or become apparent when, for a better understanding of the invention, reference is made to the following description taken in conjunction with the accompanying drawings, which show. a preferred embodiment thereof and in which:

FIG. 1 is an elevational view in cross section showing an icemaker turntable embodying the present electric drive with overload release;

FIG. 2 is an elevational view similar to FIG. 1, but showing only a gearmotor present in the electric drive;

FIG. 3 is a bottom plan view of the gearmotor which is taken along the section lines IIIIII of FIG. 2 and with the gear case removed, showing the gearing in face view from the underside;

FIG. 4 is an elevational view taken along the section line IV-IV of FIG. 3, showing among others the overload release elements inverted and in side elevation;

FIGS. 5 and 6 are respective exploded and unexploded views showing the overload release elements inverted and i side elevation; and

FIG. 7 is a plan view, actually in top plan as installed, of the overload release elements of FIGS.'4, 5, and 6.

More particularly in FIGS. 1 and 2 of the drawings, a gearmotor assembly 10 is shown connected to the turntable mechanism 12 of an ice cube maker 14. The assembly 10 produces constant speed rotary electric drive for the ice cube maker, the illustrated form and other forms of which find commercial application in home refrigerators, for example. The driven turntable turns on its vertical rotational'axis indicated by a broken line, and the direction is according to the arcuate arrow appearing in FIG. 1 and corresponding to clockwise rotation as viewed in top plan, not shown.

The electric motor of the assembly 10 runs synchronously, e.g., at 400 r.p.m., and for the purpose carries a pair of wire leads 16 supplying AC power from one of the refrigerator circuits. A gearmotor gear case 18 carries a bearing in registry with an outboard bearing 20 carried by a gear cover, not shown, and together the bearings support a depending shaft 21 joumaled therein. The shaft 21 at the bottom carries a pinion serving as the output pinion 22 of the gearmotor assembly 10.

For proper perspective right at this point, I am setting out gearmotor performance specifications by way of the following examples, simply for ease of understanding of the invention and not by way of limitation. The motor is an impedance protected, permanent magnet motor and the gearing provided therefor can, in the above example of a 400 r.p.m. motor rotor speed, afford relatively minor reduction down to the higher ultimate output speeds available which are l r.p.m. or as high as 60 r.p.m. A'motor of the general small size type herein contemplated and so geared down will, at l r.p.m. ultimate output speed, easily produce inch-ounces of torque and will stall at about inch-ounces.

In actual practice, the reduction gearing is usually fairly extensive, and overall reduction is such as to gear down the 400 r.p.m. at the rotor to as low as a revolution in 4 hours or slower. Inasmuch as the theoretical torque multiplication varies inversely to the overall speed reduction, it can be appreciated that prohibitive ultimate output torques can be produced by extensive gearing at or just short of the point of stalling out a small motor.

The turntable mechanism 12 and assembly 10 share a common horizontally disposed mounting plate 26 from which a fixed centerpost 24 of the mechanism depends. The depending centerpost 24 supports and provides a fixed journal for one independently rotatable part thereabout forming a rotor hub 28 for the mechanism, and the rotor hub 28 supports and provides a journal for one independently rotatable part thereabout forming a free turning external gear 30.

A series of radial spokes 32 integrally joins together the rotor hub which is at the inner end of the spokes and a large driven internal gear 34, which gear 34 is at the outer end of the spokes and has teeth constantly meshing with the output pinion 22. The output pinion 22 is in constant mesh with the I teeth of the free turning external gear 30, the latter of which serves as simply a pressure gear wheel or gear pressure roll backing up the pinion 22 and not transmitting any drive or doing useful work. The external gear 30 turns at a higher.

speed and in the opposite direction of rotation to the hub 28, spokes 32, and driven internal gear 34 of the turntable.

Radial arms 36 on the driven internal gear 34 are arranged in pairs each carrying one of a series of cube size, ice cups generally indicated at 38. The cups 38 are each one pivoted on the pair of carrying arms therefor to swing in the vertical plane of the pair of arms about an individual mutually transverse horizontal axis 40. A succession of chordwise disposed arm struts 42 on the turntable bridges between the pairs of radial arms 36 to impart requisite lateral rigidity to the arms.

The turntable mechanism 12 steadily moves. In the desired way it revolves the series of equally spaced cups 38 of which three with identifying subscripts are shown, illustrating all principal functions they have in making and dumping ice cubes into a refrigerator bin, not shown. Specifically, an ice cup designated 38a is shown as it moves into the partially inverted dump station position, pivoted about 110 downwardly from horizontal on its pivot axis 40. An ice cube occupying the cup 38a at the time falls therefrom into storage in the bin, leaving the cup empty. Fixed guides, not shown, in a cage below the path of revolution of the cups cam the cup 380 outwardly so as to assume a normal horizontal attitude by the time it has progressed to the next station position.

An ice cup designated 38b occupies the next position, which isthe water-fill station position and in which the cup is automatically filled by a tap with water sufficient to make an ice cube. The rest of the revolved. positions of the cups are all located in freezing stationsas examplified by the position of a cup 380. The entire contents of each cup are solidly frozen by the time it in turn reaches the dump station position of the cup 38a, and cups in all various freezing station positions about the turntable are omitted except 38b to simplify the showing.

GEARMOTOR DETAILS-FIGS. 3 AND 4 In respect of the gearmotor details as shown in these figures, the motor of the gearmotor assembly has a protruding motor shaft 44 carrying a motor shaft pinion 46. Thereadjacent is a splitter gear 48 meshing both with the pinion 46 and with an intermediate gear 50. The intermediate gear 50 is fixed to a wide pinion 52 meshing with a spring clutch gear 54. The gear 54 supports for relative rotation and frictionally engages a spring clutch 56. The clutch 56 affords slip drive in known way and swingably carries a run-detector sprag 58. The wide pinion 52 has a fixed axis of rotation and the teeth thereof are squarely in the arcuate nutational path of the sprag 58.

Upon start-up, the motor of the gearmotor reaches synchronous speed either by locking-in with each of the alternate half cycles for rotation in one direction or by locking in with each of the remaining half cycles for opposite rotation from the AC power. The motor preferably provides sustained unidirectional drive in a direction of rotation such that the sprag 58 withdraws from the wide pinion 52. Specifically, the sprag 58 withdraws to an extreme point abutting the inside of the gearcase (not shown in FIG. 3), a point at which the slipping spring clutch 56 thereafter maintains the sprag.

The difficulty with this random operation is that the motor can start up in the unwanted direction, and the spring clutch 54 will thereupon drive the sprag into the teeth of the wide pinion 52. The sprag is made of spring metal and the effect is the sprag acts as a sprag brake, stopping the motor at least once and forthwith rebounding from the teeth. One or more of the motor-stop and rebound motions are necessary in order for the motor to lose synchronism and restart on an opposite half of the cycles, so as to run unidirectionally as desired.

In providing the main power path from the motor shaft pinion 46, the splitter gear 48 driven thereby is coupled by a permanent magnet clutch 60 to a coaxial pinion 62 meshing with a counterclockwise (turning) gear 64. Although the clutch has a force field actively doing the coupling normally, the path of the force field in the clutch opens under overload because of breakage in the lines of magnetic force.

The gear 64 is fixed to a pinion 66 meshing with an intermediate gear 68. The gear 68 is fixed to a pinion 70 meshing with a counterclockwise second gear 72.

The gear 72 is fixed to a pinion 74 meshing with an intermediate 2d gear 76. The gear 76 is fixed to a pinion 78 meshing with a counterclockwise 3d gear 80 located near the end of the power path. That gear 80 is fast to the previously described, depending output shaft 21 which drives the pinion, not shown, serving as the output pinion 22 of the gearmotor assembly.

When unidirectionally rotating in the way desired, the motor shaft pinion 46, the counterclockwise gear 64, the counterclockwise second gear 72, the counterclockwise third gear 80, and the output shaft 21 are each turning counterclockwise as viewed in FIG. 3. All pinions and gears of the gearmotor turn on nonrotatable axles 82 downstanding from a gear cover 84, with certain exceptions such as the pinion and gear made fast respectively to that shaft 44 and to that shaft 21 which serve as live axles in the gearmotor.

CLUTCHES 56 VS. 60-FIGS. 3 AND 4 The spring clutch 56, slipping or driving as the occasion demands, is characterized by low cost in the expected way and is adequate to the occasion because an inexpensive slip drive device will suffice. The friction therein is low at the most and uniformity in the friction afforded is not critical.

Novelty is felt to reside in the permanent magnet clutch 60 in its unique application as disclosed herein, however. Importantly, it eliminates nonuniformity of maximum output torque such as characterizes the spring clutch whose surfaces change in their resistance to sliding and whose output torque therefore changes. More importantly in the drive hereof, the permanent magnet clutch 60 while slipping is not only exerting stall torque consistently precisely within a close maximum rated range, but is also in actuality exerting cycles which consistently reach a maximum rated slip torque in the drive line.

So when an impediment stalls the load and the gearmotor gearing, the motor continues running at synchronous speed and through the clutch 60 is constantly active to elastically load, unload, and reversely load the gearing consistently up to what the gearing can tolerate. Thus the motor, with no chance it will do stripping or other damage to the gears, will be systematically doing the most possible to cause the load to release, or to release and discharge, the impediment and to re-start in normal manner from the alternating urgings of the motor.

The novel structure and action of the magnet clutch will now be explained in detail.

CLUTCH STRUCTURE 60FIGS. 5, 6, AND 7 These figures of drawing show the structure of the clutch 60, the operating clutching element of which is an inertia member comprising a permanent bar magnet 86. The other element of the clutch is the driving member 88 formed by a mutilated cup of ferromagnetic metal or equivalent.

The splitter gear 48 and the pinion 62 driven thereby are of markedly different gear size to provide the necessary reduction ratio in the train and have a fairly thin space between the two gears. The two gears are arranged with the clutch 60 in the space therebetween, and with the adjacent gear hubs relatively rotatably supported by hollow shafts 90 and 96 disposed one within another.

More specifically, the driving member 88 of the clutch is held rotatively in balance with the large gear 48 by means of the inner one 90 of the hollow shafts which is made fast thereto by crimpings 94 on the shaft located at its upper end as viewed in FIG. 5. The magnet 86 of the clutch is held rotatively in balance with the small gear 62 by means of the outer one 96 of the hollow shafts which is fast to the former by virtue respectively of lower crimpings 96 and of being an integral extension of the small gear.

The hollow shafts are on a spindle fixed perpendicular to the cover 84 and forming one of the dead axles 82 referred to. By means of running fits, the shaft arrangement is on an axis 100 such that the inner hollow shaft 90 is concentrically supported by and journaled upon the axle 82 referred to, and the outer hollow shaft 92 is concentrically supported by and journaled upon the inner hollow shaft 90. To a great extent if not wholly so, the various materials from which the environmental parts 48, 62, 82, 84, 90, and 92 are constructed either are, or have the less-than-ferromagnetic properties of, metals such as brass or bronze so that the environment of the clutch 60 will exert minimal effect if any on the magnetic field, now to be described.

The bar magnet 86 has diametric poles of opposite algebraic sign identified by the customary N-S indicia. The magnet mechanically functions as a relatively heavy core member when the magnet as finally installed fits within the companion clutch driving member 88.

With its referred to mutilated cup form, the driving member 88 of the clutch presents two semi cylindrical wall pieces. The two wall pieces impart a C-shape to the member as viewed in cross section and serve as the necessary pole pieces 98 coextensively radially confronting the corresponding outwardly projecting magnet poles N-S when the magnet fits within the member 88 in the described way. When so fitted up, the assembled clutch has a general D-shape as viewed in cross section and as viewed in side elevation (FIG. 6).

The referred to magnetic lines of force on which the clutch depends for its basic lzl drive transmitting operation establish therein a relatively strong rotating linking field in space. The bar magnet 86 usually lags a few degrees behind the rotating pole pieces because of the torque load normally transmitted. The lines of force are simulated by the arrows 102 in FIGS. 6 and 7. The arrows indicate an essentially closed path of circulation of the field in parallel, first, across a planar radial gap in the clutch but, secondly and mainly, across an axially extending, unformly thin, cylindrical gap. The gaps are very short but their presence is essential to insure purely non-contact coupling by the clutch. Without contact and friction, there are no coupling surfaces to wear or heat up, and no friction changes or surface changes to contend with.

In an important but less usual phase of operation of the clutch, the magnetic field elastically stores up energy upon start up, at the time at which the sprag brakes the motor to a stop if the latter is running in the unwanted direction at the time. So right at that point while the moving magnet continues to run (actually to overrun), the pole pieces take a reverse direction of rotation and assume the leading position in the new direction. The new direction is counterclockwise as indicated by an arcuate arrow in FIG. 7, wherein the magnet is shown in a broken line position S and the respective pole pieces 98 are shown in solid lines. As the motor continues running undirectionally in the desired way the bending lines of force will stop and then reverse the magnet 86, while the motor keeps the pole pieces movingin the direction of the counterclockwise arrow.

The clutch thus reverses its rotation in two stages, the inertia member thereof delaying for the period of energy build-up whereas the motor and the driving member 88 will earlier have simultaneously reversed their direction of rotation. The field then reintroduces the stored energy back into the system because, as the lines of force restraighten themselves out, they cause the lagging magnetic poles at least nearly to catch up and overlappingly realign with the pole pieces 98 of the clutch driving member 88. 7

But of more importance is another phase of the clutch operation, the stalled out phase. In that phase, the stalled magnet 86 elastically stores magnetic energy rapidly in the clutch gaps during the attempt of the receding pole pieces to draw the magnet into the same direction of rotation as the pole pieces, and just as rapidly releases the energy back into the system during movement of approach of the pole pieces to the magnet to draw the magnet into taking the opposite direction of rotation.

The consequent magnetic attraction rotationally tugs on the magnet first in one direction and then the other. So as long as the drive line stays stalled, the periodically distorted and broken magnetic field will continue exerting cycles which consistently reach a maximum rated slip torque on the magnet 86 in both drive and reverse directions to one another in the drive line.

The magnet clutch 60 has the property always to slip at or above a transmitted torque when precisely in a narrowly limited range. The motor torque is not the important fact in that regard, at least not directly so because the direct torque of the motor is manifestly low. As indicated, the torque multiplication of the gearmotor gearing is the important fact. Thus in case a 400 r.p.m. motor is geared down to drive the final gear at approximately l/10 r.p.m., the final gear for present purposes will normally safely transmit up to nearly 250 inchounces of torque, for example, but is not designed for fully that much torque or over, without failing. And yet in the foregoing case, the torque if unlimited when applied to the final gear as it turns at 1/10 r.p.m. would amount to about 1,500 inch=ounces and cause immediate failure.

The particular safeguard to take in an icemaker to prevent the above difficulty can readily be appreciated at this point. A permanent magnet clutch installed ahead of the final gear in accordance with the principles of my invention affords the necessary accurate overload protection for the final gear and obviates gear failure as and if the icemaker jams. The point of installation optimumly is at or closely adjacent the input end of the gearing, where the magnet clutch speed is necessarily high and hence the torque need not be so high.

While various applications and similarly stringent conditions of operation can be easily visualized to take advantage of the principles of my invention,.the invention is primarily contemplated for use with timer-size electric motors specifically and small electric motors in general. The outside diameter of the case of such motors usually does not exceed 2 inches and the diameter of the motors is readily designed to be closer to about 1 inch.

The gearrnotor assemblies as a matter of practical importance are standardized in the respect of taking one such motor for any number of overall stages of reduction, i.e., the stages required for the particular installation under contemplation. The flexibility to do so comes in the precision to match the magnet clutch to the installation. Thus no matter what ultimate output torque would be theoretically delivered, the precise strength and location of the clutch selected is what is determinative of the loading of the final stages of gearing. So irrespective of what-the standard motor output is, the portion of that output which can be coupled to the final stages when the load stalls is accurately kept down to the limit they can safely transmit and no more.

What is claimed is:

1. For use with an icemaker assembly in which a series of cups having water-fill, freeze, and dump stations is revolved turntable-style by a motor through a drive line containing a train of speed reducing gearing with an output:

the combination, in said train, of motor driven input gear means, at least a plurality of which are enmeshed, and among which coaxial first and second power transmission gears in the input are disposed with the hubs supported for relative rotation and with a space between the planes of the gears; and

a permanent magnet coupling in said space, an operating clutching element of which is an inertia element fast to the first gear and another element of which is fast to the second gear, and mutually effectively slipping upon stalling out and interrupting power transmission so as precisely to uniformly sustain an average output torque rating for re-starting and effectively recoupling the drive elastically therefrom thence through the reducing gearing to the gearing output in the drive line.

2. The invention of claim 1, the respective operating clutching element and other element of said coupling characterized by:

bar magnet means in rotational balance with the first gear,

and pole pieces in rotational balance with the'second gear and coacting with the bar magnet means to maintain a closed path for magnetic force lines when coupling under normal load, there being an opening of said path under overload causing breakage of the magnetic lines of force aforesaid.

3. The invention of claim 2, in further combination with support means whereby the hubs of the first and second gears are supported in the described way, the gears of said combination each being relatively less-than-ferromagnetic and the rest of the combination being relatively ferromagnetic to at least the extent of each of the pole pieces and bar magnet means.

4. The invention of claim 2, characterized by:

first and second gears which have a size difference to provide a gear ratio between input and output, and the large one of which constitutes the second gear, the other coupling element comprising a mutilated cup of which the remaining portions of the cup side walls form the pole pieces aforesaid, the bar magnet means of the operating clutching element being nonrotatable to the small gear and arranged as a core member fitting in, and relatively rotatable to, the mutilated cup, and further arranged with the magnetic poles thereof each corresponding to a pole piece formed by the cup side wall portions.

5. For use with an icemaker assembly in which a series of pivoted dumping cups having water-fill, freeze, and dump stations is unidirectionally revolved turntable-style by an electric motor through a drive line containing a speed reducing train of gearing:

the combination of meshing, motor driven input gears in said train;

run-detector sprag means having first means of connection to the input gears and effective as a rebounding sprag brake to cause abrupt stop of the motor from an unestablishing the non-contact space field connection aforesaid with a pole piece driven by said gearing. 7. The invention of claim 5, the first means of connection characterized by: a spring clutch; the spring clutch and magnetic space field of the first and second means of connection being proportioned and arranged to constitute respectively low coupling torque and high coupling torque drive input elements. 8. The invention of claim 7, the clutch characterized by a weak spring. 

1. For use with an icemaker assembly in which a series of cups having water-fill, freeze, and dump stations is revolved turntable-style by a motor through a drive line containing a train of speed reducing gearing with an output: the combination, in said train, of motor driven input gear means, at least a plurality of which are enmeshed, and among which coaxial first and second power transmission gears in the input are disposed with the hubs supported for relative rotation and with a space between the planes of the gears; and a permanent magnet coupling in said space, an operating clutching element of which is an inertia element fast to the first gear and another element of which is fast to the second gear, and mutually effectively slipping upon stalling out and interrupting power transmission so as precisely to uniformly sustain an average output torque rating for re-starting and effectively recoupling the drive elastically therefrom thence through the reducing gearing to the gearing output in the drive line.
 2. The invention of claim 1, the respective operating clutching element and other element of said coupling characterized by: bar magnet means in rotational balance with the first gear, and pole pieces in rotational balance with the second gear and coacting with the bar magnet means to maintain a closed path for magnetic force lines when coupling under normal load, there being an opening of said path under overload causing breakage of the magnetic lines of force aforesaid.
 3. The invention of claim 2, in further combination with support means whereby the hubs of the first and second gears are supported in the described way, the gears of said combination each being relatively less-than-ferromagnetic and the rest of the combination being relatively ferromagnetic to at least the extent of each of the pole pieces and bar magnet means.
 4. The invention of claim 2, characterized by: first and second gears which have a size difference to provide a gear ratio between input and output, and the large one of which constitutes the second gear, the other coupling element comprising a mutilated cup of which the remaining portions of the cup side walls form the pole pieces aforesaid, the bar magnet means of the operating clutching element being nonrotatable to the small gear and arranged as a core member fitting in, and relatively rotatable to, the mutilated cup, and further arranged with the magnetic poles thereof each corresponding to a pole piece formed by the cup side wall portions.
 5. For use with an icemaker assembly in which a series of pivoted dumping cups having water-fill, freeze, and dump stations is unidirectionally revolved turntable-style by an electric motor through a drive line containing a speed reducing train of gearing: the combination of meshing, motor driven input gears in said train; run-detector sprag means having first means of connection to the input gears and effective as a rebounding sprag brake to cause abrupt stop of the motor from an unwanted run direction undertaken at random and a restart thereof in the single direction desired; and an inertia member in said train with the gears having second means of connection thereto and effective to couple the drive elastically therefrom to the drive line; the elasticity provided in the coupling characterized by a rotatable linking field in space free from causing direct physical contact in the connection and created by permanent magnetism.
 6. The invention of claim 5, the inertia member characterized by: a rotatably mounted permanent magnet magnetically establishing the non-contact space field connection aforesaid with a pole piece driven by said gearing.
 7. The invention of claim 5, the first means of connection characterized by: a spring clutch; the spring clutch and magnetic space field of the first and second means of connection being proportioned and arranged to constitute respectively low coupling torque and high coupling torque drive iNput elements.
 8. The invention of claim 7, the clutch characterized by a weak spring. 